In the past, atrial arrhythmias have been largely undertreated due to the perception that these arrhythmias are relatively benign. As more serious consequences of persistent atrial arrhythmias have come to be understood, such as an associated risk of relatively more serious ventricular arrhythmias and stroke, there is a greater interest in providing implantable atrial or dual chamber cardioverter defibrillators for treating atrial arrhythmias.
Atrial fibrillation (AF) can be treated with relatively high voltage defibrillation shocks, which are generally painful to the patient, or high frequency burst pacing. Atrial flutter (AFL), also referred to herein as atrial tachycardia (AT) can be treated by anti-tachycardia pacing therapies, high frequency burst pacing or cardioversion shocks. Generally, it is preferred to initially treat AFL with a less aggressive therapy, such as anti-tachycardia pacing or burst pacing which are not painful to the patient and require less battery energy than cardioversion shocks. A tiered therapy approach is often taken in treating atrial arrhythmias, beginning with less aggressive therapies and, if these fail, progressing to more aggressive therapies.
Some patients experience persistent atrial arrhythmias that are refractory to arrhythmia therapies. Persistent AT or AF may be sustained continuously or return soon after being terminated. A persistent atrial arrhythmia may have undesirable effects on the ventricular rate. Relatively slow, organized AT is often accompanied by elevated ventricular rate. Methods proposed for controlling the ventricular rate during an atrial arrhythmia include ventricular pacing and vagal stimulation. See for example U.S. Pat. No. 5,792,193 issued to Stoop, U.S. Pat. No. 6,434,424 issued to Igel et al., and U.S. Pat. No. 5,916,239 issued to Geddes, et al.
A slowing of the ventricular rate has been observed clinically when AT is converted to AF. An opportunity may exist, therefore, for controlling the ventricular rate by accelerating the atrial rate during persistent atrial arrhythmias. While the primary goal in delivering arrhythmia therapies is to terminate an arrhythmia, there remains a need for controlling ventricular rate when persistent atrial arrhythmias remain refractory to arrhythmia therapies.